Standard · Adhesion, cure and holidays
ISO 29601
Assessment of porosity (pinholes and holidays) in a dry paint film.
ISO 29601 sets how to find porosity, meaning pinholes, holidays and other discontinuities, in protective paint systems on steel and other conductive metals. A second edition came out in 2026 and replaced the 2011 edition.
Low or high voltage
The choice depends on the mean dry film thickness of the non-conductive layers. A low-voltage wet-sponge detector is the default for thinner films, and a high-voltage DC detector for thicker ones. The 2026 edition changed how the high-voltage test voltage is calculated, in line with the recent ASTM and AMPP holiday-testing standards.
The trap
Only the non-conductive layers count. A zinc-rich primer, galvanizing or thermally sprayed metal under the paint conducts, so its thickness is left out of the thickness that sets the method and the voltage.
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This page describes the subject of ISO 29601 in our own words; it does not reproduce the standard. For the full text, buy the current edition from ISO. Checked on 2026-10-14; errors go in the corrections log. CoatMentor is an independent study aid. It is not affiliated with ISO, AMPP, SSPC, NACE International, ASTM or FROSIO.